Methane fluxes and rice yields as a function of sulfate fertilizer with incorporated rice stubble

A trial was conducted by applying different sulfate (SO4) rates on methane (CH4) emissions and grain yields (GY) in a field with recently incorporated rice stubble (IRS), 7.5 t ha-1. Ammonium phosphate SO4 fertilizer (42% SO4) was applied at the rates of 0, 50, 100, and 210 kg SO4 ha-1. The whole field was kept flooded with irrigation water. The results showed that the impact of SO4 on CH4 emissions weakened through the stages of rice growth. High daily CH4 fluxes at the reproductive stage governed the quantities of seasonal CH4 emission (SME), and led to a high ratio of SME/IRS. Only the highest rate of 210 kg SO4 ha-1 could reduce SME by 66.9%. The highest GY was 4.08 t ha-1 at 100 kg SO4 ha-1. The whole experiment gave high values of SME/GY and SME/IRS. To reduce CH4 emission without adverse effects on GY, split application of SO4 at 100-155 kg SO4 ha-1 with the last application preferably during the late tillering stage should be tested, along with incorporating rice stubble into the soil immediately after harvest.